1. Field of the Invention
The present invention relates to a process and a plant for laying a pipe in a trench.
2. Description of Related Art
Conventionally, pipes are made either of steel or of a composite composed especially of a filamentary tubular structure, for example based on glass fibers, which is impregnated with a curable resin, especially a resin which is curable under the effect of heat. The pipes are produced from elementary tube sections of predetermined length, for example 12 meters; by way of indication, their outside diameter is generally between 300 and 1 000 mm.
Steel pipes are produced by butt welding a large number of sections; they are then covered with a corrosion-protection coating. When the fluids transported are highly corrosive, an internal coating must also be provided.
Pipes made of a composite are advantageously used when the corrosion problems are very considerable, and do not allow the use of steel pipes. Such pipes are also produced conventionally starting from tubular sections of given length, for example 12 m, which are connected and fastened, end to end, generally by screwing, the final assembly being completed by adhesive bonding. Such pipes are very expensive, in particular because of the need to machine the ends in order to join the pipe sections end to end.
Of course, this conventional assembly technique poses transportation problems. In general, the pipes, are transported to the installation site by trucks, and the number of pipes transported is limited by their weight and their volume. Thus, if sections having a diameter of 500 mm are being dealt with, it is possible to transport only about ten pipes 12 m in length (i.e. in total approximately 120 m of pipe) per truck. To lay a pipe 2 000 m in length, more than 16 trucks will consequently be required, corresponding to a total transported weight of 240 tonnes. Furthermore, joining the pipes end to end is a lengthy, tedious and tricky task; for a length of 2,000 m, more than 150 joints would be required.
The relevant prior art may be illustrated by the documents FR-2 155 485 and EP-0 856 694.
The subject of FR-2 155 485 is a plant intended for laying pipes. The technique described in that document consists in using, as initial preform, a flattened and soft hose, made of a curable material, for example a synthetic polymer resin which includes a heat-activated crosslinking catalyst. The flattened hose is wound on a reel.
On the site, the reel is, unwound and the hose made round and cured, progressively as the pipe is deposited on the ground. An expanding tool, composed of two spheres, which is fitted into the pipe as it leaves the reel, has the function of making the hose “round”, that is to say giving it a cylindrical shape, while a device for curing the wall is used immediately after the rounding operation; curing is obtained especially” by spraying the pipe with a liquid agent, of suitable composition and at a suitable temperature.
Document EP-0 856 694 describes a process which starts with a preform in the form of a flattened hose, the wall of which includes a fibrous reinforcement, such as a filamentary tubular structure, which is impregnated with a curable, for example thermally curable, resin. The tubular preform is stored in the flattened state, for example on a drum (or reel), and is brought onto the site in this state. The hose, which may be of great length, is laid in the trench in this flattened state and is then “made round” due to the effect of internal pressure generated by a liquid, for example water, introduced into the hose. Next the resin is cured, so as to obtain a cylindrical and rigid pipe.
The process according to document FR-A-2 155 485 raises practical difficulties insofar as it is very difficult for the double-sphere expanding tool, which is provided inside the preform and allows it to be made round, to be properly held in place.
The process according to document EP-0 856 694 requires the use of a pressurized liquid, such as water, to make the preform round once it has been deposited in the trench; the process is tricky and relatively tedious to implement; in any case, it requires the liquid in question to be available on site.
Moreover, these known techniques use a preform whose wall has already been provided with resin, the latter being incorporated into the wall in the factory during manufacture of the preform. The presence of this resin influences the weight and volume of the preform, even if it is in the flattened state. In addition, with regard to a thermosetting resin, storing it at room temperature for a long period may initiate the crosslinking of the polymer. This undesirable premature crosslinking may modify the behavior of the resin, or even prevent it from being used.
It is therefore necessary with the known devices to keep the preform, and the resin that it contains, in a container at a controlled temperature, including during transportation; this poses, of course, practical and cost problems.
The present invention aims to solve these difficulties.